The present invention relates to magnetic data storage and retrieval systems. More particularly, the present invention relates to a device for resetting the biasing magnetization of a biasing element in a magnetic sensor.
In an electronic data storage and retrieval system, a magnetic recording head typically includes a reader portion having a sensor for retrieving magnetically encoded information stored on a magnetic medium. Magnetic flux from the surface of the medium causes rotation of the magnetization vector of a sensing layer or layers of the sensor, which in turn causes a change in the electrical properties of the sensor. The sensing layers are often called free layers, since the magnetization vectors of the sensing layers are free to rotate in response to external magnetic flux. The change in the electrical properties of the sensor may be detected by passing a current through the sensor and measuring a voltage across the sensor. External circuitry then converts the voltage information into an appropriate format and manipulates that information as necessary to recover information encoded on the medium.
The sensor must be stabilized against the formation of edge domains because domain wall motion results in electrical noise that makes data recovery impossible. A common way to achieve stabilization is with a permanent magnet abutted junction design in which permanent magnet bias elements abut opposite sides of the sensor. Permanent magnets have a high coercive field (i.e., are magnetically hard). The magnetostatic field from the permanent magnets stabilizes the sensor, prevents edge domain formation, and provides proper bias.
As the magnetic sensor is exposed to the magnetic field from the magnetic medium, the permanent magnets may experience high frequency agitation from the field. This agitation opposes the intrinsic residual flux of the permanent magnets, which causes randomization of the magnetic domains of the permanent magnets. As a result, the magnetization strength of the permanent magnets may degrade over time, causing destabilization of domain walls and increased electrical noise in the free layer.